Annular fluids, also known as packer fluids or insulating packer fluids, are liquids which are pumped into annular openings such as, for example, (1) between a wellbore wall and a casing, (2) between adjacent, concentric strings of pipe extending into a wellbore, or (3) into the bore of a cased wellbore. In the completion of oil and gas wells, it is currently the practice to place aqueous or non-aqueous hydrocarbon based fluids, such as packer fluids, into a casing annulus above a packer, specifically where the packer has been set to isolate production fluid from the casing annulus. Packer fluids, introduced into the casing annulus around a production pipe, fill the annular column to surface. Packer fluids are utilized for various reasons, such as, to provide both pressure stability and thermal protection to the casing annulus of production oil and gas wells as well as in injection wells, to provide hydrostatic pressure to lower pressure across the sealing element and to equalize pressure relative to the formation, to lower differential pressure on the wellbore and/or casing to prevent collapse, and to protect metals and elastomers from corrosion. Packer fluids may further be used to control heat loss, both conductive and convective heat losses. Thus, insulating packer fluids may be utilized in oil or gas well construction operations conducted in low temperature venues of the world, for example, those areas having permafrost.
Heavy oil production is an operation which often can benefit from the use of an insulating packer fluid. In heavy oil production, a high-pressure steam or hot water is injected into the well and the oil reservoir to heat the fluids in the reservoir, causing a thermal expansion of the crude oil, an increase in reservoir pressure and a decrease of the oil's viscosity. In this process, damage to the well casing may occur when heat is transferred through the annulus between the well tubing and the casing. The resulting thermal expansion of the casing can break the bond between the casing and the surrounding cement, causing leakage. Accordingly, an insulating medium such as a packer fluid may be used to insulate or to help insulate the well tubing. The packer fluid also reduces heat loss and saves on the energy requirements in stimulation using hot-water or steam (huff-n-puff) or in hot-water- or steam-flooding.
In addition to steam injection processes and operations which require production through a permafrost layer, subsea fields, such as in deep water, 1,500 to more than 6,000 feet deep, require specially designed systems, which may utilize an insulating packer fluid. For example, a subsea oil reservoir temperature may be between about 120° F. and 250° F., while the temperature of the water through which the oil may be conveyed is often as low as 32° F. to 50° F. Conveying the high temperature oil through such a low temperature environment can result in oil temperature reduction and consequently the separation of the oils into various hydrocarbon fractions and the deposition of paraffins, waxes, asphaltenes, and gas hydrates. The agglomeration of these oil constituents can cause blocking or restriction of the wellbore, resulting in a reduction or even catastrophic failure of the production operation.
Thus, there exist a need for compositions, such as packer fluids, for example, exhibiting good yield stress and long-term stability in high temperature environments.